The invention relates to a lock catch for double doors in which door-mounted holding elements are cooperable with lock catch locking elements and wherein a spring within the catch housing biases the locking elements into their closing position, the holding element of one door being blocked in its closing position when the holding element of the other door is also brought into its closing position. With a lock catch as described, both doors can be closed only in a certain sequence and can be opened again only in the reverse sequence.
Britsh Pat. No. 1,254,392 discloses a lock catch of the above mentioned kind which ensures the closing function. In this known lock catch the two locking elements are formed as slides which maintain within the catch housing in the closing positions by means of a compression spring. The catch housing is fastened to the frame of the doors so that the displacement direction of the slides is parallel to the open front of the door frame. The slides protrude from the catch housing by a triangular ratchet tip. On the doors, holding elements are fastened which have a triangular detent. When one door is closed, its holding element displaces the corresponding slide counter to the force of the spring, until the slide engages with the detent of the holding element in the closed position of the door. To block the door which is closed first, another slide is displaceably guided in the catch housing, this slide being displaced by the holding element of the second door. When the second door is brought into the closing position, the displaced second slide prevents a displacement of the slide associated with the first door, which slide thus blocks the holding element of the first door. Therefore, the first door can be opened only after the last-closed door has been opened and when the holding element on the first door releases its associated slide.
This known lock catch, however, has the disadvantage that the closed doors do not closely abut the front edges of the door frame. As the slide and holding elements have a ratchet position defined in the closing direction, tolerances of the door, of the frame and in the attachment of the catch housing and of the holding elements cannot be compensated.
To overcome the shortcomings noted above, attempts have been made to design the holding elements as inclined ratchet elements engageable over the triangular ratchet tips from behind. In this way, a part of the spring force acting on the slides is transformed into an attractive force component which pulls the closed door against the frame for the door. Since the ratchet flaps can only be very short, the holding elements and the catch housing must be mounted on the doors and on the door frame very precisely. Since the slides are pushed against the ratchet flaps with great force and acts on a large area, the preponderant part of the attractive force component is thereby cancelled out.
It is an object of the invention to provide a lock catch of the above mentioned kind which is of relatively simple construction, can easily be fastened to the door frame and the doors, and yet chieves positive locking action, compensation of the parts and attachment tolerances and maintains blocking of the door which is closed first.